1. Field of the Invention
The present invention relates to an image projection apparatus to which a projection optical system is interchangeably attached, particularly to an image projection apparatus including a shift mechanism of the attached projection optical system.
2. Description of the Related Art
Image projection apparatuses, such as a liquid crystal projector and a micromirror projector, project light modulated by a light modulation element such as a liquid crystal panel or a digital micromirror device onto a projection surface such as a screen through a projection optical system such as a projection lens to display an image. Such image projection apparatuses are also used for multi-screen projection that projects a large screen image produced by connecting plural images projected by plural image projection apparatuses, the connection being made by adjoining of edges of the projected images, by overlapping of near-edge areas thereof and the like.
In the multi-screen projection, making the connection portions of the mutually adjacent projected images unnoticeable may require fine tuning of positions of the projected images with a pixel unit smaller than one pixel (for example, 0.5 pixel unit).
Such fine tuning of the projected image position is enabled by a shift mechanism that moves (shifts) the projection optical system in a direction orthogonal to its optical axis with respect to the light modulation element. The shift mechanism moves a holding member to which a lens barrel that houses the projection optical system therein is fixed (the projection optical system and the lens barrel are hereinafter collectively referred to as “a projection lens”), with a shift actuator such as a motor, with respect to a base member that is fixed to a chassis or the like of the image projection apparatus.
However, an image projection apparatus to which plural types of projection lenses such as a wide-angle lens and a telephoto lens are selectively (interchangeably) attached and which also includes the shift mechanism has the following problem. The plural types of projection lenses have mutually different weights or mutually different shift sensitivities (that is, positional change amounts of the projected image on the projection surface to a same movement amount of the projection lens). Therefore, even though control of the shift actuator is performed with a same control condition (same control parameter), the movement amount of the projection lens or an actual movement amount of the projected image is changed according to the weight or the shift sensitivity of the attached projection lens.
Japanese Patent No. 4401499 discloses an image projection apparatus that changes a parameter for controlling a shift actuator depending on a type of an attached interchangeable projection lens. This image projection apparatus allows attachment of plural types of projection lenses whose image circle sizes are mutually different. Specifically, this image projection apparatus distinguishes the type of the attached projection lens and changes a shift position (parameter) to stop drive of the shift actuator so as to limit a shiftable range of the attached projection lens to a range appropriate for the image circle thereof.
However, the image projection apparatus disclosed in Japanese Patent No. 4401499 does not consider that the movement amount of the projection lens or the projected image is changed depending on the weight or the shift sensitivity of the attached projection lens even though the shift actuator is controlled with the same control condition.